1. Field
An embodiment of the present invention relates to a broadcasting communication module, and more particularly, to a receiver optical module structure
2. Description of the Related Art
An optical receiver module (or a receiver optical module) may include an optical signal input unit, a photoelectric conversion unit, a high frequency signal amplifying/processing unit, and a high frequency signal output unit. In particular, an optical receiver module receiving a signal of 10 Gbps or higher should be designed and manufactured in consideration of loss, reflection, and resonance of a high frequency signal with respect to module components and a layout structure of the components. Meanwhile, in order to electrically connect the components, wire bonding or flipchip bonding using solder may be used. Here, when a connection structure passing through a wire or solder from a high frequency signal is not proper, impedance mismatch of a transmission signal is brought about to degrade high frequency signal characteristics of an optical module.
In particular, in order to smoothly operate a photodetector of a photoelectric conversion unit with radio frequency, a return path is required to be present in a ground of a high frequency signal in an area sufficiently adjacent to the photodetector. In this case, the return path of the high frequency signal may be formed by using a capacitor element, and characteristics of a high frequency output signal may be sensitively changed according to a length or shape of wire bonding between an optical receiver and the capacitor element.
When a capacitor is integrated within an adjacent wiring circuit board or within a photodetector, an optical receiver module may obtain excellent high frequency signal characteristics. However, generally, techniques of integrating a capacitor within a wiring circuit board adjacent to a photodetector or within a photodetector are not easily applied and incur high cost. For example, in a capacitor-integrated photodetector, a large capacitor pad may be formed on a photodetector board through a semiconductor process. However, as a large insulating layer and metal layer process is added, process yield is degraded and a size of a chip is also increased by an area of the capacitor, increasing cost.
Meanwhile, a structure of a photodetector used for optical communication may be generally classified into a plane-incident photodetector (PIN-PD) and a waveguide photodetector. The waveguide photodetector has an operation speed higher than that of the PIN-PD, and thus, the waveguide photodetector may be advantageous for a high speed communication device.
However, in case of an optical module using a multi-channel waveguide photodetector, it is difficult to uniformly form wiring between photodetectors and electric elements and layout thereof on a two-dimensional plane in every channel. In a case where a capacitor is not integrated in a photodetector, the capacitor should be disposed on a side surface of a waveguide photodetector. In this case, however, a length and a shape of bonding wire of each channel are varied, resulting in that it may be difficult to obtain uniform high frequency characteristics for each channel
In a receiver optical module, LC resonance may be generated by a photodetector, a capacitor and a bonding wire between the photodetector and the capacitor, by which 3 dB band width characteristics of an OE response of a module can be enhanced. In general, a photodetector may dominantly specify a capacitor value, and a bonding wire may dominantly affect an inductance value. In particular, since an inductance value is determined according to a bonding form and length of a bonding wire, it is important to perform a wire bonding process with a uniform length in order to obtain multi-channel signals with uniform quality.
Meanwhile, a ground may be classified into a high frequency signal ground and a case ground. A ground in a circuit path of a signal may be classified as a signal ground (GND for signal), and an external case may be classified as a case ground. Ideal ground impedance has a potential of 0V, but a signal ground may have a potential difference according to an area and a position in a high frequency. In order to minimize the potential difference, it may be required to form a ground pattern as large as possible and, further, it may be required to form a ground adjacent to an element sensitive to noise in the form of a conductive block and manufactured to be adjacent to a package ground.